Mix the coconut milk: combine coconut milk, whole milk, sugar, and salt in a large bowl or pitcher; stir until sugar dissolves. Taste and add sugar if needed. Cover and refrigerate at least 1 hour until thoroughly chilled.
Prep the fruit: cut jackfruit into thin strips and young coconut meat into similar ribbons. Drain palm seeds, nata de coco, and canned fruit completely.
Soak the basil seeds (if using): stir into cold water, rest 10 minutes until they swell into clear beads, then drain.
Assemble: divide crushed ice among six tall glasses. Layer in jackfruit, coconut meat, palm seeds, nata de coco, and fruit cocktail — a handful of each per glass. Pour cold sweetened coconut milk over, filling to about 3/4 of each glass. Top with basil seeds and red rubies if using.
Serve immediately with long spoons and wide straws, stirring once or twice before eating.